Some electronic devices use transducers to convert electrical signals into motion or to exert a force. These transducers may be electromechanical, microelectromechanical systems (MEMS), acoustic, piezoelectric, etc. One example of this type of device is a print head, in which a transducer is activated by an electronic signal to cause ink to exit the print head through a jet or nozzle. In some examples, when the system activates the transducer with an electrical signal the transducer actuates and displaces a diaphragm or other structure that in turn causes the ink to pass through the jet onto a printing substrate.
In devices that utilize these types of transducers, such as ink jet print heads, a non-conductive adhesive standoff typically exists to hold electrical contact pads on a flexible circuit or rigid circuit board in proximity to the transducer elements. Because the adhesive standoff is non-conductive, it must posses a hole or other gap over the actuator to allow electrical interconnect to the transducer. The interconnect typically consists of a conductive adhesive placed in the opening in the standoff, in contact with the pads on the circuit element and in contact with the actuator elements, providing electrical continuity between them. A typical example of the conductive adhesive would be a silver-loaded epoxy.
The conductive epoxy is rigid in the cured state and may provide an undesirable mechanical coupling to the circuit element and between transducers. Mechanical coupling of the transducer to the circuit element results in mechanical loading of the actuator and reduced motion for a fixed voltage driving it. In many cases increasing the voltage to the actuator will compensate for the mechanical loading, but is undesirable. A second result of the mechanical coupling between the circuit element and the actuators is ‘cross talk’ or accidental alteration of the behavior of neighboring transducers to an activated transducer.
Other, softer, conductive adhesives seem to eliminate the mechanical cross talk, but have reduced reliability in thermal cycling. Thermal cycling figures significantly in design considerations in solid ink jet printers, as heat is applied throughout the system to keep the ink in its liquid/molten state and heat is removed when the system is turned off.
The loading of the transducer by the conductive adhesive and the circuit element typically has some variability across an array. This leads to differing deflections within the array, resulting in different drop masses of the ink drops and different speeds. This variability, if uncorrected, has negative impact on image quality
Anisotropic conducting films (ACF) are widely used in flat panel display technology as the interconnect between a circuit element and display elements. These films typically have low or no conductivity in the X-Y plane that typically has large dimensions compared to the thickness but have high conductivity along the third axis, often labeled the Z-axis. As a result, these are also sometimes referred to as Z-axis conducting films. The base film may consist of a thermoset plastic, a thermoplastic, a thermoplastic adhesive or a thermoset adhesive. The film provides a matrix for electrically conducting elements that are dispersed in the film that span the z-axis and provide the electrical conduction through the film. The anisotropy of the conductivity is the result of having the conducting elements in low enough concentration that they only infrequently touch to provide limited lateral conductivity. The conducting elements are typically small metal balls, metal coated polymer balls, or oriented thin metal rods. These interconnects are normally used with stationary electrical elements and are therefore not normally concerned with the mechanical loading of a transducer.